1. Field of the Invention
The present invention relates to the field of fluid flow control valves and more particularly a valve having a movable closure that effects sealing engagement with the valve seat ring during only a small increment of the valve closure movement.
2. Background Art
Because the present invention is described in the context of a ball-type valve, the prior art will also be primarily discussed in that same context. It being understood that the present invention is defined and limited solely by the claims and not by the description.
The use of a rotating spherical plug or ball valve to control flow of fluid is known and old in the art. See for example U.S. Pat. No. 3,067,978 to Natho which discloses a conventional top entry ball valve. As disclosed therein, the rotatable ball closure element outer spherical surfaces establishes continuous sealing contact with fixed annular valve seats to control flow through the valve. The ball closure element is provided with a central flow port and is rotated through a quarter turn or 90.degree. arc between open and closed positions to control the flow. When the ball flow port is substantially aligned with the valve housing flow passages the valve is operated to the open position providing a substantially unrestricted straight thru fluid flow path. When the ball is rotated to closed position the flow port traverse or perpendicular to the flow passage of the ball closure element serves as a stopper to block fluid communication and place the valve in the closed position. During operating movement of the ball, sliding contact occurs between the ball and seat providing the continuous seal.
To seal between the outer spherical surface of the ball member and the valve body for directing all flow through the ball flow port various forms of annular seat means may be employed. Known conventional seat means employed include both compression seats (Natho) and axial floating seats, such as disclosed in U.S. Pat. No. 3,214,135 to Hartmann. Floating seats may also be made pressure energized or responsive to enhance sealing. In sealingly engaging the ball to effect the continuous seals the seats are a source of great frictional resistance to operating rotation of the ball valve. Such frictional resistance is greatly increased by the force resulting from unbalanced contained fluid pressure when opening the valve. Such unbalanced pressure in the case of pressurized seats further increase the frictional contact force. In addition the large seat to ball contact pressure tends to score or otherwise damage the sealing faces during sliding contact which effectively destroys the seal therebetween.
Due to their relatively fast response or operation (90.degree. rotation or quarter turn) and compact annular dimension relative to size of flow path advantage, ball valves have also been tailored for subsurface use in wells as well as in conventional valve housing. For example see the subsurface ball valve construction of U.S. Pat. Nos. 3,007,669 (Fredd) and 3,385,701 (Potts). These valves also have high frictional resistance by the seats to ball movement.
To reduce the frictional and pressure forces tending to prevent rotation of the ball and avoid damage to the valve seats and ball, a number of approaches have been attempted in the prior art.
One approach to reduce the force of the sliding contact has been to vent or equalize the pressure differential forces across the closed ball prior to commencing rotation to the open position. For examples of this pressure balancing or equalizing approach in the prior art see the following U.S. Pat. Nos.:
3,414,061, Nutter PA1 3,993,136, Mott PA1 4,293,038, Evans PA1 4,332,267, Evans PA1 3,398,928, Fredd PA1 4,210,207, McStavick et al PA1 4,270,606, McStavick et al PA1 4,508,173, Read PA1 2,076,841, Heggem PA1 2,516,947, Blevans PA1 2,719,022, Blevans PA1 3,473,554, King PA1 3,512,546, King
Another approach has been to employ relatively complex operating mechanisms to effect rotational operation of the ball with a minimum of internal friction. Typical of such prior art mechanisms, which have not been widely accepted commercially due to their complexity and cost, are the following U.S. Pat. Nos.:
Another approach, using selectively expandable valve closure members for engaging a fixed valve seat ring are also known. U.S. Pat. No. 3,497,180 to Ryey discloses such arrangement in a butterfly valve.
A variation to the Ryey approach applicable to ball valves has been to employ a segmented ball that moves axially as well as rotationally. For an example of such approach, see U.S. Pat. No. 1,803,773 to Schmidt et al. To control axial outward and inward movement of the plates or calottes carried by the ball to engage the fixed valve seats a relatively complex mechanical sequencing arrangement is employed. To operate the valve the stem is rotated 180.degree. or half a circle to operate the valve. During half of this arc of the operating stem, the ball is locked to the stem for rotating the ball 90.degree. or a quarter turn between positions. During the other 90.degree. portion of the stem movement, the ball is unlocked from the stem and cams or eccentric guides are used to radially extend or retract the ball segment plates from sealing engagement with the fixed seats. Such complex operating arrangement is located in the flow passage where it is subject to malfunctioning and is costly to produce.
U.S. Pat. No. 2,711,302 to McWhorter discloses an operating mechanism for successively unseating, rotating and reseating a tapered plug closure assembly. In seating and unseating the tapered plug slides across the face of the valve seats which tends to score or damage the sealing capability of the seats.
Another approach has been to employ a ball closure or valve core member that is spaced from a single fixed valve seat with the ball moving longitudinally or axially in the final increment of movement when rotated into the closed position to sealingly engage the seat. Such an arrangement is disclosed in the following U.S. Pat. Nos.:
One significant drawback to this approach is that the valve is not reversible and can reliably control fluid flow in only a single direction.
Such an arrangement of interrupted seat engagement is also not limited to ball valves as it does have limited application to other types of valves. See for example U.S. Pat. No. 3,119,594 to Heggem entitled "Swing Gate Valve" in which the closure member is held open by fluid flow.
Each of the above mentioned U.S. patents is hereby fully incorporated by this specific reference as if they were set forth in full in this disclosure. While the forgoing patented inventions were improvements over the prior art, there remains an unsatisfied need for a relatively simple and inexpensive quick acting valve, controllable in operation and that effects both upstream and downstream sealing to control flow in either direction.